1. Field of the Invention
The present invention relates to a lens drive control apparatus that is incorporated in an optical instrument such as a camera, etc.
2. Description of the Related Art
A typical and conventional lens drive control apparatus is provided with a code plate on which a code pattern corresponding to the position of the movable lens is formed, and with a brush synchronized with the motion of a movable lens which reads the code pattern of the code plate. The brush reads the code pattern data and detects the position of movable lens. This type of lens drive control system using the code plate can detect the lens position more accurately if spaces in the code pattern become narrower, thereby the movement control of movable lens can be done more accurately. However, narrowing of the spaces in the code pattern requires the increase of number of codes.
An increase in the number of codes not only requires a larger size of code plate, but also a wider space for providing such a larger sized code plate as well as an increased number of signal cables connected thereto. A wider space for the code plate would result in undesirably large apparatus, therefore the number of codes need to be minimized. A decreased number of codes can be accomplished by, e.g., using relative codes having repeated patterns, however, the relative codes would sometimes be read inaccurately. Furthermore, a normal type of movable lens is provided with a stopper at which further movement of the movable lens is mechanically prohibited, and if the movable lens erroneously reads the code and collides against this stopper, an operator would sense an unpleasant jolt or noise, and can sometimes result in the camera being damaged.
It is an object of the present invention to provide a lens drive control apparatus in which accurate drive control of movable lens can be performed via a simple structure.
To achieve the object mentioned above, a lens drive control apparatus is provided, including a movable lens which is movable along the optical axis; a lens driver which moves the movable lens; a code plate having two limit positions respectively serving as mechanical movement limit positions of the movable lens, the code plate including first codes corresponding to each of a plurality of predetermined stop positions at which the movable lens is stopped between the two limit positions, and second codes corresponding to each of predetermined positions respectively provided between the limit positions and the plurality of predetermined stop positions; a code detector which moves together with the movable lens in order to detect the first and second codes; a pulse generator which generates pulses according to the movement of the movable lens; a pulse counter which counts the number of pulses generated by the pulse generator; and a position determining device which determines an absolute position of the first code detected by the code detector, based on the number of pulses counted by the pulse counter from the time when the code detector detects one of the first code and second code until the time when the code detector detects the subsequent other of the second code and first code, while the lens driver moves the movable lens toward one of the two limit positions.
In an embodiment, each of the first codes and second codes includes a plurality of detection zones, each detection zone of the plurality of detection zones having a predetermined length with respect to the direction of movement of the movable lens. The pulse counter counts the number of pulses based on one of a moment when the code detector detects an extremity of a detection zone of the plurality of detection zones, and a moment when the code detecting state of the code detector changes from one of a detecting state to non-detecting state and a non-detecting state to a detecting state.
Preferably, the code detector is provided with a first code detector and a second code detector which independently detect the first codes and second codes, respectively.
In an embodiment, the position determining device determines an absolute position of the first code detected by the code detector, based on the number of pulses generated by the pulse generator, from a moment when the code detector detects the change of detecting state of the second code from a non-detecting state to a detecting state until a moment when the code detector detects the change of detecting state of the first code from a non-detecting state to a detecting state.
In an embodiment, one of the two limit positions is provided at a shortest position at which the movable lens can be positioned at a shortest distance from an image plane formed by an imaging optical system including the movable lens, and another of the two limit positions is provided at a longest position at which the movable lens can be positioned at a longest distance from the image plane.
In an embodiment, the imaging optical system includes a step zoom lens which changes the focal length thereof by moving the movable lens and by stopping the movable lens at each stop position of the plurality of predetermined stop positions.
In an embodiment, each distance between each of the first codes or each distance between each of the second codes are not equal to each other.
In an embodiment, the code plate is provided with the second code -between the first code corresponding to the longest position and the first code corresponding to the stop position closest to the longest position.
In an embodiment, either the length in the direction of movement of the movable lens or the number of pulses generated by the pulse generator, with respect to only a detection zone of the second code provided between the first code corresponding to the longest position and the first code corresponding to the stop position closest to the longest position, is different from that of the other detection zones of the second code.
In an embodiment, either the length in the direction of movement of the movable lens or the number of pulses generated by the pulse generator, with respect to only the detection zone of the second code provided between the first code corresponding to the longest position and the first code corresponding to the stop position closest to the longest position, is respectively one of longer and greater than that of the other detection zones of the second code. While the code detector detects the second codes during movement of the movable lens toward the longest position via the lens driver, the position determining device determines that the movable lens has gone beyond the stop position at the longest position when the number of pulses generated by the pulse generator becomes larger than a predetermined number.
In an embodiment, the movable lens is a zoom lens which changes the focal length by zooming from a maximum wide-angle position and subsequently stops at each of the stop positions, wherein the stop position of the zoom lens which is closest to the shortest position is determined as the maximum wide-angle position. Only the length of the second code positioned between the first code corresponding to the stop position closest to the longest position and the first code corresponding to the stop position closest to the longest position is different from the length of the other second codes, with respect to the direction of movement of the movable lens. While the code detector detects the second codes during movement of the zoom lens toward the longest position via the lens driver, the position determining device determines that the zoom lens has gone beyond a maximum telephoto position when the number of pulses generated by the pulse generator becomes larger than a predetermined number.
In an embodiment, while the lens driver moves the movable lens from the shortest position toward the longest position, the position determining device determines that the movable lens reaches the stop position adjacent to the stop position of the shortest position when the code detector detects the first code subsequent to generation of a predetermined number of pulses by the pulse generator.
In an embodiment, the second code is also provided at the position corresponding to a shortest position of the movable lens closest to a image plane formed by an imaging optical system including the movable lens.
In an embodiment, the movable lens is a step zoom lens which can change the focal length thereof by moving the movable lens to any one of the stop positions and performing a focusing operation in a zone between the stop position and the subsequent stop position in the direction of the longest position. The second code also serves as a reference position for focusing control by the step zoom lens.
In an embodiment, the first codes and the second codes are arranged in parallel, and the code detector detects the first codes and the second codes.
In an embodiment, the first codes and second codes have repeated patterns of a binary code of ON and OFF.
Preferably, the first code is used for detecting the focal length of the step zoom lens, and the second code is used for detecting the position of the focusing position of the step zoom lens.
In an embodiment, the pulse counter is reset when the second code is detected by the code detector, and wherein the pulse counter counts the pulse according to the movement of the step zoom lens between the each stop position, of the plurality of predetermined stop positions, detected by the first code.
In an embodiment, the code detecting state of the code detector is the same, with respect to the first code and the second code, when the movable lens is positioned at the shortest position.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-264112 (filed on Aug. 31, 2000) which is expressly incorporated herein in its entirety.